Superoxide dismutase--mentor of abiotic stress tolerance in crop plants

Metal and metal oxide nanoparticles-induced reactive oxygen species: Phytotoxicity and detoxification mechanisms in plant cell

Nanotechnology is advancing rapidly in this century and the industrial use of nanoparticles for new applications in the modernization of different industries such as agriculture, electronic, food, energy, environment, healthcare and medicine is growing exponentially. Despite applications of several nanoparticles in different industries, they show harmful effects on biological systems, especially in plants. Various mechanisms for the toxic effects of nanoparticles have already been proposed; however, elevated levels of reactive oxygen species (ROS) molecules including radicals [(e.g., superoxide (O2•‒), peroxyl (HOO•), and hydroxyl (HO•) and non-radicals [(e.g., hydrogen peroxide (H2O2) and singlet oxygen (1O2) is more important. Excessive production/and accumulation of ROS in cells and subsequent induction of oxidative stress disrupts the normal functioning of physiological processes and cellular redox reactions. Some of the consequences of ROS overproduction include peroxidation of lipids, changes in protein structure, DNA strand breaks, mitochondrial damage, and cell death. Key enzymatic antioxidants with ROS scavenging ability comprised of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), peroxidase (POD), and glutathione reductase (GR), and non-enzymatic antioxidant systems including alpha-tocopherol, flavonoids, phenolic compounds, carotenoids, ascorbate, and glutathione play vital role in detoxification and maintaining plant health by balancing redox reactions and reducing the level of ROS. This review provides compelling evidence that phytotoxicity of nanoparticles, is mainly caused by overproduction of ROS after exposure. In addition, the present review also summarizes the intrinsic detoxification mechanisms in plants in response to nanoparticles accumulation within plant cells.

Cyclopropanation and membrane unsaturation improve antibiotic resistance of swarmer Pseudomonas and its sod mutants exposed to radiations, in vitro and in silico approch

It was known that UVc irradiation increases the reactive oxygen species' (ROS) levels in bacteria hence the intervention of antioxidant enzymes and causes also changes in fatty acids (FAs) composition enabling bacteria to face antibiotics. Here, we intended to elucidate an interrelationship between SOD and susceptibility to antibiotics by studying FA membrane composition of UVc-treated P. aeruginosa PAO1 and its isogenic mutants (sodM, sodB and sod MB) membrane, after treatment with antibiotics. Swarmer mutants defective in genes encoding superoxide dismutase were pre-exposed to UVc radiations and then tested by disk diffusion method for their contribution to antibiotic tolerance in comparison with the P. aeruginosa wild type (WT). Moreover, fatty acid composition of untreated and UVc-treated WT and sod mutants was examined by Gaz chromatography and correlated to antibiotic resistance. Firstly, it has been demonstrated that after UVc exposure, swarmer WT strain, sodM and sodB mutants remain resistant to polymixin B, a membrane target antibiotic, through membrane unsaturation supported by the intervention of Mn-SOD after short UVc exposure and cyclopropanation of unsaturated FAs supported by the action of Fe-SOD after longer UVc exposure. However, resistance for ciprofloxacin is correlated with increase in saturated FAs. This correlation has been confirmed by a molecular docking approach showing that biotin carboxylase, involved in the initial stage of FA biosynthesis, exhibits a high affinity for ciprofloxacin. This investigation has explored the correlation of antibiotic resistance with FA content of swarmer P.aeruginosa pre-exposed to UVc radiations, confirmed to be antibiotic target dependant.

Biochemical responses of Echinochloa polystachya inoculated with a Trichoderma consortium during the removal of a pyrethroid-based pesticide

The biochemical response of plants exposed to pesticides and inoculated with microorganisms is of great importance to explore cleaning up strategies for contaminated sites with pyrethroid-based pesticides. We evaluated the effects of a Trichoderma consortium on the biochemical responses of Echinochloa polystachya plants during the removal of a pyrethroid-based pesticide. Plants were inoculated or not with the Trichoderma consortium and exposed to commercial pesticide H24®, based on pyrethroids. Pesticide application resulted in significant reduction in root protein content (58%), but enhanced content of malondialdehyde (MDA) in shoots, superoxide dismutase (SOD) activity in shoots and roots, and catalase (CAT) activity in roots. Inoculation of Trichoderma consortium in E. polystachya exposed to the pesticide resulted in increased protein content in roots and MDA content in shoots (2-fold). Trichoderma consortium improved protein content and SOD activity (140-fold) in plants. Fungal inoculation increased the removal (97.9%) of the pesticide in comparison to the sole effect of plants (33.9%). Results allow further understanding about the responses of the interaction between plants and root-associated fungi to improving the assisted-phytoremediation of solid matrices contaminated with organic pesticides.

Response of photosynthetic characteristics and antioxidant system in the leaves of safflower to NaCl and NaHCO3

KEY MESSAGE

Compared with NaCl, NaHCO3 caused more serious oxidative damage and photosynthesis inhibition in safflower by down-regulating the expression of related genes. Salt-alkali stress is one of the important factors that limit plant growth. NaCl and sodium bicarbonate (NaHCO3) are neutral and alkaline salts, respectively. This study investigated the physiological characteristics and molecular responses of safflower (Carthamus tinctorius L.) leaves treated with 200 mmol L-1 of NaCl or NaHCO3. The plants treated with NaCl treatment were less effective at inhibiting the growth of safflower, but increased the content of malondialdehyde (MDA) in leaves. Meanwhile, safflower alleviated stress damage by increasing proline (Pro), soluble protein (SP), and soluble sugar (SS). Both fresh weight and dry weight of safflower was severely decreased when it was subjected to NaHCO3 stress, and there was a significant increase in the permeability of cell membranes and the contents of osmotic regulatory substances. An enrichment analysis of the differentially expressed genes (DEGs) using Gene Ontology and the Kyoto Encyclopedia of Genes and Genomes identified significant enrichment of photosynthesis and pathways related to oxidative stress. Furthermore, a weighted gene co-expression network analysis (WGCNA) showed that the darkgreen module had the highest correlation with photosynthesis and oxidative stress traits. Large numbers of transcription factors, primarily from the MYB, GRAS, WRKY, and C2H2 families, were predicted from the genes within the darkgreen module. An analysis of physiological indicators and DEGs, it was found that under saline-alkali stress, genes related to chlorophyll synthesis enzymes were downregulated, while those related to degradation were upregulated, resulting in inhibited chlorophyll biosynthesis and decreased chlorophyll content. Additionally, NaCl and NaHCO3 stress downregulated the expression of genes related to the Calvin cycle, photosynthetic antenna proteins, and the activity of photosynthetic reaction centers to varying degrees, hindering the photosynthetic electron transfer process, suppressing photosynthesis, with NaHCO3 stress causing more pronounced adverse effects. In terms of oxidative stress, the level of reactive oxygen species (ROS) did not change significantly under the NaCl treatment, but the contents of hydrogen peroxide and the rate of production of superoxide anions increased significantly under NaHCO3 stress. In addition, treatment with NaCl upregulated the levels of expression of the key genes for superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), the ascorbate-glutathione cycle, and the thioredoxin-peroxiredoxin pathway, and increased the activity of these enzymes, thus, reducing oxidative damage. Similarly, NaHCO3 stress increased the activities of SOD, CAT, and POD and the content of ascorbic acid and initiated the glutathione-S-transferase pathway to remove excess ROS but suppressed the regeneration of glutathione and the activity of peroxiredoxin. Overall, both neutral and alkaline salts inhibited the photosynthetic process of safflower, although alkaline salt caused a higher level of stress than neutral salt. Safflower alleviated the oxidative damage induced by stress by regulating its antioxidant system.

Superoxide Dismutase Premodulates Oxidative Stress in Plastids for Protection of Tobacco Plants from Cold Damage Ultrastructure Damage

ROS-dependent induction of oxidative damage can be used as a trigger initiating genetically determined non-specific protection in plant cells and tissues. Plants are potentially able to withstand various specific (toxic, osmotic) factors of abiotic effects, but do not have sufficient or specific sensitivity to form an adequate effective response. In this work, we demonstrate one of the possible approaches for successful cold acclimation through the formation of effective protection of photosynthetic structures due to the insertion of the heterologous FeSOD gene into the tobacco genome under the control of the constitutive promoter and equipped with a signal sequence targeting the protein to plastid. The increased enzymatic activity of superoxide dismutase in the plastid compartment of transgenic tobacco plants enables them to tolerate the oxidative factor of environmental stresses scavenging ROS. On the other hand, the cost of such resistance is quite high and, when grown under normal conditions, disturbs the arrangement of the intrachloroplastic subdomains leading to the modification of stromal thylakoids, probably significantly affecting the photosynthesis processes that regulate the efficiency of photosystem II. This is partially compensated for by the fact that, at the same time, under normal conditions, the production of peroxide induces the activation of ROS detoxification enzymes. However, a violation of a number of processes, such as the metabolism of accumulation, and utilization and transportation of sugars and starch, is significantly altered, which leads to a shift in metabolic chains. The expected step for further improvement of the applied technology could be both the use of inducible promoters in the expression cassette, and the addition of other genes encoding for hydrogen peroxide-scavenging enzymes in the genetic construct that are downstream in the metabolic chain.

Exogenous Cytokinin 4PU-30 Modulates the Response of Wheat and Einkorn Seedlings to Ultraviolet B Radiation

Abiotic stress is responsible for a significant reduction in crop plant productivity worldwide. Ultraviolet (UV) radiation is a natural component of sunlight and a permanent environmental stimulus. This study investigated the distinct responses of young wheat and einkorn plants to excessive UV-B radiation (180 min at λmax 312 nm) following foliar pretreatment with 1 µM synthetic cytokinin 4PU-30. Results demonstrated that UV radiation significantly amplified hydrogen peroxide levels in both wheat and einkorn, with einkorn exhibiting a more pronounced increase compared to wheat. This elevation indicated the induction of oxidative stress by UV radiation in the two genotypes. Intensified antioxidant enzyme activities and the increased accumulation of typical stress markers and non-enzyme protectants were evidenced. Transcriptional activity of genes encoding the key antioxidant enzymes POX, GST, CAT, and SOD was also investigated to shed some light on their genetic regulation in both wheat and einkorn seedlings. Our results suggested a role for POX1 and POX7 genes in the UV-B tolerance of the two wheat species as well as a cytokinin-stimulated UV-B stress response in einkorn involving the upregulation of the tau subfamily gene GSTU6. Based on all our findings, it could be concluded that 4PU-30 had the potential of alleviating oxidative stress by attenuating the symptoms of superfluous UV-B illumination in the two examined plant species.

Amaranth's Growth and Physiological Responses to Salt Stress and the Functional Analysis of AtrTCP1 Gene

Amaranth species are C4 plants that are rich in betalains, and they are tolerant to salinity stress. A small family of plant-specific TCP transcription factors are involved in the response to salt stress. However, it has not been investigated whether amaranth TCP1 is involved in salt stress. We elucidated that the growth and physiology of amaranth were affected by salt concentrations of 50-200 mmol·L-1 NaCl. The data showed that shoot and root growth was inhibited at 200 mmol·L-1, while it was promoted at 50 mmol·L-1. Meanwhile, the plants also showed physiological responses, which indicated salt-induced injuries and adaptation to the salt stress. Moreover, AtrTCP1 promoted Arabidopsis seed germination. The germination rate of wild-type (WT) and 35S::AtrTCP1-GUS Arabidopsis seeds reached around 92% by the seventh day and 94.5% by the second day under normal conditions, respectively. With 150 mmol·L-1 NaCl treatment, the germination rate of the WT and 35S::AtrTCP1-GUS plant seeds was 27.0% by the seventh day and 93.0% by the fourth day, respectively. Under salt stress, the transformed 35S::AtrTCP1 plants bloomed when they grew 21.8 leaves after 16.2 days of treatment, which was earlier than the WT plants. The transformed Arabidopsis plants flowered early to resist salt stress. These results reveal amaranth's growth and physiological responses to salt stress, and provide valuable information on the AtrTCP1 gene.

From swamp to field: how genes from mangroves and its associates can enhance crop salinity tolerance

Salinity stress is a critical challenge in crop production and requires innovative strategies to enhance the salt tolerance of plants. Insights from mangrove species, which are renowned for their adaptability to high-salinity environments, provides valuable genetic targets and resources for improving crops. A significant hurdle in salinity stress is the excessive uptake of sodium ions (Na+) by plant roots, causing disruptions in cellular balance, nutrient deficiencies, and hampered growth. Specific ion transporters and channels play crucial roles in maintaining a low Na+/K+ ratio in root cells which is pivotal for salt tolerance. The family of high-affinity potassium transporters, recently characterized in Avicennia officinalis, contributes to K+ homeostasis in transgenic Arabidopsis plants even under high-salt conditions. The salt overly sensitive pathway and genes related to vacuolar-type H+-ATPases hold promise for expelling cytosolic Na+ and sequestering Na+ in transgenic plants, respectively. Aquaporins contribute to mangroves' adaptation to saline environments by regulating water uptake, transpiration, and osmotic balance. Antioxidant enzymes mitigate oxidative damage, whereas genes regulating osmolytes, such as glycine betaine and proline, provide osmoprotection. Mangroves exhibit increased expression of stress-responsive transcription factors such as MYB, NAC, and CBFs under high salinity. Moreover, genes involved in various metabolic pathways, including jasmonate synthesis, triterpenoid production, and protein stability under salt stress, have been identified. This review highlights the potential of mangrove genes to enhance salt tolerance of crops. Further research is imperative to fully comprehend and apply these genes to crop breeding to improve salinity resilience.

C. S, Anil VS, Raghavan S. Phytosynthesis of silver nanoparticles using aqueous sandalwood (Santalum album L.) leaf extract: Divergent effects of SW-AgNPs on proliferating plant and cancer cells

The biogenic approach for the synthesis of metal nanoparticles provides an efficient eco-friendly alternative to chemical synthesis. This study presents a novel route for the biosynthesis of silver nanoparticles using aqueous sandalwood (SW) leaf extract as a source of reducing and capping agents under mild, room temperature synthesis conditions. The bioreduction of Ag+ to Ago nanoparticles (SW-AgNPs) was accompanied by the appearance of brown color, with surface plasmon resonance peak at 340-360 nm. SEM, TEM and AFM imaging confirm SW-AgNP's spherical shape with size range of 10-32 nm. DLS indicates a hydrodynamic size of 49.53 nm with predominant negative Zeta potential, which can contribute to the stability of the nanoparticles. FTIR analysis indicates involvement of sandalwood leaf derived polyphenols, proteins and lipids in the reduction and capping of SW-AgNPs. XRD determines the face-centered-cubic crystalline structure of SW-AgNPs, which is a key factor affecting biological functions of nanoparticles. This study is novel in using cell culture methodologies to evaluate effects of SW-AgNPs on proliferating cells originating from plants and human cancer. Exposure of groundnut calli cells to SW-AgNPs, resulted in enhanced proliferation leading to over 70% higher calli biomass over control, enhanced defense enzyme activities, and secretion of metabolites implicated in biotic stress resistance (Crotonyl isothiocyanate, Butyrolactone, 2-Hydroxy-gamma-butyrolactone, Maltol) and plant cell proliferation (dl-Threitol). MTT and NRU were performed to determine the cytotoxicity of nanoparticles on human cervical cancer cells. SW-AgNPs specifically inhibited cervical cell lines SiHa (IC50-2.65 ppm) and CaSki (IC50-9.49 ppm), indicating potential use in cancer treatment. The opposing effect of SW-AgNPs on cell proliferation of plant calli (enhanced cell proliferation) and human cancer cell lines (inhibition) are both beneficial and point to potential safe application of SW-AgNPs in plant cell culture, agriculture and in cancer treatment.

Features of the Effect of Quercetin on Different Genotypes of Wheat under Hypoxia

Hypoxia is one of the common abiotic stresses that negatively affects the development and productivity of agricultural crops. Quercetin is used to protect plants from oxidative stress when exposed to environmental stressors. O2 deficiency leads to impaired development and morphometric parameters in wheat varieties Orenburgskaya 22 (Triticum aestivum L.) and varieties Zolotaya (Triticum durum Desf.). Cytological analysis revealed various types of changes in the cytoplasm under conditions of hypoxia and treatment with quercetin. The most critical changes in the cytoplasm occur in the Zolotaya variety during pretreatment with quercetin followed by hypoxia, and in the Orenburgskaya 22 variety during hypoxia. Quercetin has a protective effect only on the Orenburgskaya 22 variety, and also promotes a more effective recovery after exposure to low O2 content. Hypoxia causes an increase in reactive oxygen species and activates the antioxidant system. It has been shown that the most active components of the antioxidant system in the Orenburgskaya 22 variety are MnSOD and Cu/ZnSOD, and in the Zolotaya variety GSH. We have shown that quercetin provides resistance only to the wheat genotype Orenburgskaya 22, as a protective agent against abiotic stress, which indicates the need for a comprehensive study of the effects of exogenous protectors before use in agriculture.

Identification and characterization of the critical genes encoding Cd-induced enhancement of SOD isozymes activities in Zhe-Maidong (Ophiopogon japonicus)

Superoxide dismutase (SOD) protects plants from abiotic stress-induced reactive oxygen species (ROS) damage. Here, the effects of cadmium (Cd) exposure on ROS accumulation and SOD isozymes, as well as the identification of significant SOD isozyme genes, were investigated under different Cd stress treatments to Zhe-Maidong (Ophiopogon japonicus). The exposure to Cd stress resulted in a notable elevation in the SOD activity in roots. Cu/ZnSODa and Cu/ZnSODb were the most critical SOD isozymes in response to Cd stress, as indicated by the detection results for SOD isozymes. A total of 22 OjSOD genes were identified and classified into three subgroups, including 10 OjCu/ZnSODs, 6 OjMnSODs, and 6 OjFeSODs, based on the analysis of conserved motif and phylogenetic tree. Cu/ZnSOD-15, Cu/ZnSOD-18, Cu/ZnSOD-20, and Cu/ZnSOD-22 were the main genes that control the increase in SOD activity under Cd stress, as revealed via quantitative PCR and transcriptome analysis. Additionally, under various heavy metal stress (Cu2+, Fe2+, Zn2+, Mn2+), Cu/ZnSOD-15, Cu/ZnSOD-18, and Cu/ZnSOD-22 gene expression were significantly upregulated, indicating that these three genes play a critical part in resisting heavy metal stress. The molecular docking experiments performed on the interaction between oxygen ion (O2•-) and OjSOD protein have revealed that the critical amino acid residues involved in the binding of Cu/ZnSOD-22 to the substrate were Pro135, Ile136, Ile140, and Arg144. Our findings provide a solid foundation for additional functional investigations on the OjSOD genes, as well as suggestions for improving genetic breeding and agricultural management strategies to increase Cd resistance in O. japonicus.

Castor (Ricinus communis L.) differential cell cycle and metabolism reactivation, germinability, and seedling performance under NaCl and PEG osmoticum: Stress tolerance related to genotype-preestablished superoxide dismutase activity

Castor (Ricinus communis) is a relevant industrial oilseed feedstock for many industrial applications, being globally mainly cultivated by smallholder farmers in semiarid areas, where abiotic stresses predominate. Therefore, susceptible to generating reactive oxygen species (ROS) and subsequent oxidative stress, compromising cell metabolism upon seed imbibition and germination, seedling and crop establishment, and yield. The present study evaluated the consequences of water restriction by Polyethylene glycol (PEG) and Sodium chloride (NaCl) on cell cycle and metabolism reactivation on germinability, seedling growth, and vigor parameters in 2 commercial castor genotypes (Nordestina and Paraguaçu). PEG water restriction inhibited germination completely at -0.23 MPa or higher, presumably due to reduced oxygen availability. The restrictive effects of NaCl saline stress on germination were observed only from -0.46 MPa onwards, affecting dry mass accumulation and the production of normal seedlings. In general, superoxide dismutase (SOD) activity increased in NaCl -0.23 MPa, whereas its modulation during the onset of imbibition (24h) seemed to depend on its initial levels in dry seeds in a genotype-specific manner, therefore, resulting in the higher stress tolerance of Nordestina compared to Paraguaçu. Overall, results show that Castor germination and seedling development are more sensitive to the restrictive effects of PEG than NaCl at similar osmotic potentials, contributing to a better understanding of the responses to water restriction stresses by different Castor genotypes. Ultimately, SOD may constitute a potential marker for characterizing castor genotypes in stressful situations during germination, early seedling, and crop establishment, and a target for breeding for Castor-improved stress tolerance.

Effect of luminescent materials on the biochemistry, ultrastructure, and rhizobial microbiota of Spirodela polyrhiza

Fluorescent materials and technologies have become widely used in scientific research, and due to the ability to convert light wavelengths, their application to photosynthetic organisms can affect their development by altering light quality. However, the impacts of fluorescent materials on aquatic plants and their environmental risks remain unclear. To assess the effects of luminescent materials on floating aquatic macrophytes and their rhizosphere microorganisms, 4-(di-p-tolylamino)benzaldehyde-A (DTB-A) and 4-(di-p-tolylamino)benzaldehyde-M (DTB-M) (emitting blue-green and orange-red light, respectively) were added individually and jointly to Spirodela polyrhiza cultures and set at different concentrations (1, 10, and 100 μM). Both DTB-A and DTB-M exhibited phytotoxicity, which increased with concentration under separate treatment. Moreover, the combined group exhibited obvious stress relief at 10 μM compared to the individually treated group. Fluorescence imaging showed that DTB-A and DTB-M were able to enter the cell matrix and organelles of plant leaves and roots. Peroxidation induced cellular damage, contributing to a decrease in superoxide dismutase (SOD) and peroxidase (POD) activities and malondialdehyde (MDA) accumulation. Decomposition of organelle structures, starch accumulation in chloroplasts, and plasmolysis were observed under the ultrastructure, disrupting photosynthetic pigment content and photosynthesis. DTB-A and DTB-M exposure resulted in growth inhibition, dry weight loss, and leaf yellowing in S. polyrhiza. A total of 3519 Operational Taxonomic Units (OTUs) were identified in the rhizosphere microbiome. The microbial communities were dominated by Alphaproteobacteria, Oxyphotobacteria, and Gammaproteobacteria, with the abundance and diversity varied significantly among treatment groups according to Shannon, Simpson, and Chao1 indices. This study revealed the stress defense response of S. polyrhiza to DTB-A and DTB-M exposures, which provides a broader perspective for the bioremediation of pollutants using aquatic plants and supports the further development of fluorescent materials for applications.

Plant growth promoting bacteria and citric acid promote growth and cadmium phytoremediation in ryegrass

Based on the growth-promoting effect of plant growth promoting bacteria on plants and the mobilization of Cd by citric acid, an experiment was designed in which the combined treatment of Bacillus megaterium and citric acid promoted ryegrass to repair Cd-contaminated soil. This study aimed to evaluate the effects of different treatments on the antioxidant enzyme activity, photosynthesis intensity, Cd accumulation, and rhizosphere cadmium migration under cadmium contamination conditions. And the soil morphology and structure changes were studied by infrared spectroscopy FourierTransformInfrared(FT-IR) and scanning electron microscope Energy Dispersive Spectrometer(SEM-EDS) before and after different treatments. The results show that the combined treatment of Bacillus megaterium and citric acid significantly improved the oxidative stress defense and plant photosynthesis and increased of rye biomass. rye biomass 1.28 times higher than CK treatment. Joint treatment significantly increased the amount of shoot accumulation of Cd, 2.31 times higher than CK treatment, increased the migration and accumulation of cadmium. FTIR and SEM-EDS also showed that the organic constituents such as O-H, C-O and C-N in soils as a major mechanism for mobilization of the heavy metal Cd. Thus, the combined treatment of Bacillus megaterium and citric acid can promote plant growth, improve the damage to ryegrass caused by single organic acid addition, and improve the plant extraction efficiency, which is a feasible way to repair Cd-contaminated soil through activated extraction system.

OsCSD2 and OsCSD3 Enhance Seed Storability by Modulating Antioxidant Enzymes and Abscisic Acid in Rice

Seed deterioration during storage poses a significant challenge to rice production, leading to a drastic decline in both edible quality and viability, thereby impacting overall crop yield. This study aimed to address this issue by further investigating candidate genes associated with two previously identified QTLs for seed storability through genome association analysis. Among the screened genes, two superoxide dismutase (SOD) genes, OsCSD2 (Copper/zinc Superoxide Dismutase 2) and OsCSD3, were selected for further study. The generation of overexpression and CRISPR/Cas9 mutant transgenic lines revealed that OsCSD2 and OsCSD3 play a positive regulatory role in enhancing rice seed storability. Subsequent exploration of the physiological mechanisms demonstrated that overexpression lines exhibited lower relative electrical conductivity, indicative of reduced cell membrane damage, while knockout lines displayed the opposite trend. Furthermore, the overexpression lines of OsCSD2 and OsCSD3 showed significant increases not only in SOD but also in CAT and POD activities, highlighting an augmented antioxidant system in the transgenic seeds. Additionally, hormone profiling indicated that ABA contributed to the improved seed storability observed in these lines. In summary, these findings provide valuable insights into the regulatory mechanisms of OsCSDs in rice storability, with potential applications for mitigating grain loss and enhancing global food security.

Mitigating chromium toxicity in rice (Oryza sativa L.) via ABA and 6-BAP: Unveiling synergistic benefits on morphophysiological traits and ASA-GSH cycle

In recent years, the use of plant hormones, such as abscisic acid (ABA) and 6-benzylaminopurine (6-BAP), has gained significant attention for their role in mitigating abiotic stresses across various plant species. These hormones have been shown to play a vital role in enhancing the ascorbate-glutathione cycle and eliciting a wide range of plant growth and biomass, photosynthetic efficiency, oxidative stress and response of antioxidants and other physiological responses. While previous research has been conducted on the individual impact of ABA and 6-BAP in metal stress resistance among various crop species, their combined effects in the context of heavy metal-stressed conditions remain underexplored. The current investigation is to assess the beneficial effects of single and combined ABA (5 and 10 μM L-1) and 6-BAP (5 and 10 μM L-1) applications in rice (Oryza sativa L.) cultivated in chromium (Cr)-contaminated soil (100 μM). Our results showed that the Cr toxicity in the soil showed a significant declined in the growth, gas exchange attributes, sugars, AsA-GSH cycle, cellular fractionation, proline metabolism in O. sativa. However, Cr toxicity significantly increased oxidative stress biomarkers, organic acids, enzymatic and non-enzymatic antioxidants including their gene expression in O. sativa seedlings. Although, the application of ABA and 6-BAP showed a significant increase in the plant growth and biomass, gas exchange characteristics, enzymatic and non-enzymatic compounds and their gene expression and also decreased the oxidative stress, And Cr uptake. In addition, individual or combined application of ABA and 6-BAP enhanced the cellular fractionation and decreases the proline metabolism and AsA-GSH cycle in rice plants. These results open new insights for sustainable agriculture practices and hold immense promise in addressing the pressing challenges of heavy metal contamination in agricultural soils.

Physiological response and phytoremediation potential of dioecious Hippophae rhamnoides inoculated with arbuscular mycorrhizal fungi to Pb and Zn pollution

Plant-microorganism combined remediation of heavy metal pollution has been reported, but little attention has been paid to the effect of arbuscular mycorrhizal (AM) fungi on phytoremediation of dioecious plants under heavy metal pollution. In this study, the growth, physiological responses and phytoremediation traits of Hippophae rhamnoides were determined to evaluate whether sex-specific ecophysiological responses and phytoremediation capacities of females and males are affected by additional AM fungi (Glomus mosseae) under heavy metal treatments. The results showed that excess Pb and Zn stresses inhibited photosynthetic capacities of both sexes. However, inoculated AM fungi treatment increased the activity of photosynthesis, content of photosynthetic pigment, activity of superoxide dismutase, the content of proline and root Pb content and enrichment coefficient of males while decreased root Pb content of females under Pb stress. On the other hand, inoculated AM fungi treatment increased the photosynthetic activities and Pro accumulation of females, and activity of superoxide dismutase and transport coefficient of males under Zn stress. These results demonstrate that H. rhamnoides inoculated AM fungi showed significant sex-specific responses on the growth, physiological traits and phytoremediation potential to Pb and Zn stress. AM fungi significantly improved the tolerance of males to Pb stress and both sexes to Zn stress, which indicates H. rhamnoides and AM fungi can be used as a plant-microbial combined remediation method for Pb and Zn contaminated soil. More attention should be paid on sexual-specific responses and phytoremediation of dioecious plants to heavy metals in the future.

Heat and Wheat: Adaptation strategies with respect to heat shock proteins and antioxidant potential; an era of climate change

Extreme changes in weather including heat-wave and high-temperature fluctuations are predicted to increase in intensity and duration due to climate change. Wheat being a major staple crop is under severe threat of heat stress especially during the grain-filling stage. Widespread food insecurity underscores the critical need to comprehend crop responses to forthcoming climatic shifts, pivotal for devising adaptive strategies ensuring sustainable crop productivity. This review addresses insights concerning antioxidant, physiological, molecular impacts, tolerance mechanisms, and nanotechnology-based strategies and how wheat copes with heat stress at the reproductive stage. In this study stress resilience strategies were documented for sustainable grain production under heat stress at reproductive stage. Additionally, the mechanisms of heat resilience including gene expression, nanomaterials that trigger transcription factors, (HSPs) during stress, and physiological and antioxidant traits were explored. The most reliable method to improve plant resilience to heat stress must include nano-biotechnology-based strategies, such as the adoption of nano-fertilizers in climate-smart practices and the use of advanced molecular approaches. Notably, the novel resistance genes through advanced molecular approach and nanomaterials exhibit promise for incorporation into wheat cultivars, conferring resilience against imminent adverse environmental conditions. This review will help scientific communities in thermo-tolerance wheat cultivars and new emerging strategies to mitigate the deleterious impact of heat stress.

Biochemical dynamics during postharvest: Highlighting the interplay of stress during storage and maturation of fresh produce

The lifecycle of fresh produce involves a sequence of biochemical events during their ontology, and these events are particularly significant for climacteric fruits. A high demand during ripening is observed in these plant products, which is reflected in a high rate of respiration and ethylene production. Increased respiratory demand triggers the activation of secondary pathways such as alternate oxidase, which do not experience critical increases in energy consumption in non-climacteric fruit. In addition, biochemical events produced by external factors lead to compensatory responses in fresh produce to counteract the oxidative stress caused by the former. The dynamics of these responses are accompanied by signaling, where reactive oxygen species play a pivotal role in fresh product cell perception. This review aims to describe the protection mechanisms of fresh produce against environmental challenges and how controlled doses of abiotic stressors can be used to improve quality and prolong their shelf-life through the interaction of stress and defense mechanisms.

Biochemical and molecular properties of Boro rice (Oryza sativa L.) cultivars under abiotic stresses

The present investigation was conducted so as to unravel the various underlying antioxidant enzyme and non-enzyme defence mechanisms in some selected Boro rice cultivars that differ in temperature stress tolerance. Oxidative injury under heat and cold stress, H2O2 level showed a decline in roots and shoots of Boro in stressed condition whilst significant rise in the susceptible varieties was observed under both the stresses. However, susceptible varieties, such as Disang (shoots), Moricha (shoots) and China Boro (roots), showed a decreased H2O2 content at recovery. Under cold stress, roots and shoots of Boro and Laal Bihari showed a decreased level of lipid peroxidises and Boro and Kolong under heat stress. In contrast, significant enhancement of lipid peroxidase was revealed in the susceptible varieties. Remarkable increase in non-enzymatic antioxidants like proline, glutathione and ascorbate content was seen in the shoots of Boro in the treated and the recovery conditions. On the other hand, in enzymatic antioxidants like ascorbate peroxidase, guaiacol peroxidase, superoxide dismutase, catalase, and glutathione reductase activity, marked enhancement in ascorbate peroxidase activity was seen in the roots and the shoots of Boro and Kolong in treated and recovery samples and decreased in Swarnabh under heat stress. The guaiacol peroxidase activity of roots and shoots increased in Boro and Kolong under heat stress, and decreased in China boro and Swarnabh. The superoxide dismutase activity in the roots and shoot of Boro increased significantly under both the stress conditions in treated and recovery. Root and shoots of Swarnabh and Moricha showed decline in SOD activity in stressed conditions. The catalase activity in the case of Boro, showed a significant increase in both its roots and shoots under cold and heat stresses in the treated and the recovery samples. Moreover, under heat stress, the root and the shoots of Boro and Kolong showed the maximum glutathione activity, whilst Swarnabh and China Boro showed reduced glutathione activity at 96 h and recovery. On the other hand, the gene expression pattern of the cold-responsive genes (OsHAN1/OsCYP9B4 and FeSOD1) showed significant upregulation in the tolerant than the sensitive cultivars. Similarly, heat-responsive genes (OsTT1/OsPAB1 and OsHsfC1b) are also highly upregulated in the tolerant than the susceptible ones. Thus, the findings would provide a thorough insight into various non-enzymatic and enzymatic antioxidants and stress-responsive genes of Boro rice that could help in the future rice breeding programmes for cold and heat stresses.

The damage caused by Cd toxicity to photosynthesis, cellular ultrastructure, antioxidant metabolism, and gene expression in young cacao plants are mitigated by high Mn doses in soil

Manganese (Mn) is one of the essential mineral micronutrients most demanded by cacao. Cadmium (Cd) is highly toxic to plants and other living beings. There are indications that Mn can interact with Cd and mitigate its toxicity. The objective of this study was to evaluate the action of Mn on the toxic effect of Cd in young plants of the CCN 51 cacao genotype, subjected to different doses of Mn, Cd, and Mn+Cd in soil, through physiological, biochemical, molecular, and micromorphological and ultrastructural changes. High soil Mn doses favored the maintenance and performance of adequate photosynthetic processes in cacao. However, high doses of Cd and Mn+Cd in soil promoted damage to photosynthesis, alterations in oxidative metabolism, and the uptake, transport, and accumulation of Cd in roots and leaves. In addition, high Cd concentrations in roots and leaf tissues caused irreversible damage to the cell ultrastructure, compromising cell function and leading to programmed cell death. However, there was a mitigation of Cd toxicity when cacao was grown in soils with low Cd doses and in the presence of Mn. Thus, damage to the root and leaf tissues of cacao caused by Cd uptake from contaminated soils can be attenuated or mitigated by the presence of high Mn doses in soil.

Combined toxic effects of polypropylene and perfluorooctanoic acid on duckweed and periphytic microorganisms

Microplastics and perfluorooctanoic acid coexist in the aquatic environment. Duckweed was exposed to a range of concentrations (0.1-1000 μg L-1) of solutions containing polypropylene (PP) and perfluorooctanoic acid (PFOA) for 14 days to measure their toxicity. The result showed the single and combined PP and PFOA treatments did not significantly influence the growth of duckweed. The greatest PP and PFOA concentrations of combined pollution affect plant chlorophyll. Moreover, the combined treatment of duckweed consistently resulted in increased malondialdehyde (MDA) levels, indicating oxidative damage. As an antioxidant stress response, the combination-treated plants were encouraged to produce superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT). Meanwhile, 3519 Operational Taxonomic Units (OTUs) were identified in the duckweed rhizosphere. Proteobacteria was the most predominant microbial community. Shannon, Simpson, and Chao1 discovered that microbial communities changed in response to single and combination PP and PFOA treatments, with decreased diversity and increased abundance. In addition, SEM analysis also revealed that the combined treatment significantly phyllosphere microorganisms. The findings of this investigation add to our knowledge of how PP and PFOA affect duckweed and the rhizospheric microorganisms, expanding the theoretical basis for employing duckweed in complex contamination.

The genetic variation in drought resistance in eighteen perennial ryegrass varieties and the underlying adaptation mechanisms

BACKGROUND

Drought resistance is a complex characteristic closely related to the severity and duration of stress. Perennial ryegrass (Lolium perenne L.) has no distinct drought tolerance but often encounters drought stress seasonally. Although the response of perennial ryegrass to either extreme or moderate drought stress has been investigated, a comprehensive understanding of perennial ryegrass response to both conditions of drought stress is currently lacking.

RESULTS

In this study, we investigated the genetic variation in drought resistance in 18 perennial ryegrass varieties under both extreme and moderate drought conditions. The performance of these varieties exhibited obvious diversity, and the survival of perennial ryegrass under severe stress was not equal to good growth under moderate drought stress. 'Sopin', with superior performance under both stress conditions, was the best-performing variety. Transcriptome, physiological, and molecular analyses revealed that 'Sopin' adapted to drought stress through multiple sophisticated mechanisms. Under stress conditions, starch and sugar metabolic enzymes were highly expressed, while CslA was expressed at low levels in 'Sopin', promoting starch degradation and soluble sugar accumulation. The expression and activity of superoxide dismutase were significantly higher in 'Sopin', while the activity of peroxidase was lower, allowing for 'Sopin' to maintain a better balance between maintaining ROS signal transduction and alleviating oxidative damage. Furthermore, drought stress-related transcriptional and posttranscriptional regulatory mechanisms, including the upregulation of transcription factors, kinases, and E3 ubiquitin ligases, facilitate abscisic acid and stress signal transduction.

CONCLUSION

Our study provides insights into the resistance of perennial ryegrass to both extreme and moderate droughts and the underlying mechanisms by which perennial ryegrass adapts to drought conditions.

Redox-mediated responses to high temperature in plants

As sessile organisms, plants are particularly affected by climate change and will face more frequent and extreme temperature variations in the future. Plants have developed a diverse range of mechanisms allowing them to perceive and respond to these environmental constraints, which requires sophisticated signalling mechanisms. Reactive oxygen species (ROS) are generated in plants exposed to various stress conditions including high temperatures and are presumed to be involved in stress response reactions. The diversity of ROS-generating pathways and the ability of ROS to propagate from cell to cell and to diffuse through cellular compartments and even across membranes between subcellular compartments put them at the centre of signalling pathways. In addition, their capacity to modify the cellular redox status and to modulate functions of target proteins, notably through cysteine oxidation, show their involvement in major stress response transduction pathways. ROS scavenging and thiol reductase systems also participate in the transmission of oxidation-dependent stress signals. In this review, we summarize current knowledge on the functions of ROS and oxidoreductase systems in integrating high temperature signals, towards the activation of stress responses and developmental acclimation mechanisms.

Physiological and transcriptome analysis of Dendrobium officinale under low nitrogen stress

Nitrogen (N) is the main nutrient of plants, and low nitrogen usually affects plant growth and crop yield. The traditional Chinese herbal medicine Dendrobium officinale Kimura et. Migo is a typical low nitrogen-tolerant plant, and its mechanism in response to low nitrogen stress has not previously been reported. In this study, physiological measurements and RNA-Seq analysis were used to analyse the physiological changes and molecular responses of D. officinale under different nitrogen concentrations. The results showed that under low nitrogen levels, the growth, photosynthesis and superoxide dismutase activity were found to be significantly inhibited, while the activities of peroxidase and catalase, the content of polysaccharides and flavonoids significantly increased. Differentially expressed genes (DEGs) analysis showed that nitrogen and carbon metabolisms, transcriptional regulation, antioxidative stress, secondary metabolite synthesis and signal transduction all made a big difference in low nitrogen stress. Therefore, copious polysaccharide accumulation, efficient assimilation and recycling of nitrogen, as well as rich antioxidant components play critical roles. This study is helpful for understanding the response mechanism of D. officinale to low nitrogen levels, which might provide good guidance for practical production of high quality D. officinale .

Accumulation Potential Cadmium and Lead by Sunflower (Helianthus annuus L.) under Citric and Glutaric Acid-Assisted Phytoextraction

Organic acid assistance is one of the effective methods for phytoremediation of heavy metal contaminated soil. In this experiment, the addition of citric and glutaric acids was selected to improve the accumulation of cadmium and lead by Helianthus annuus L. Results showed that citric and glutaric acids elevated the growth of the plants and stimulated Cd/Pb uptake by plant in single Cd/Pb treatments, but glutaric acid showed inhibitory action on the uptake of metals in complex treatments. Organic acids impacted the translocation of Cd/Pb differently, and citric acids (30 mg·L^-1) enhanced the translocation of Cd to aerial parts of the plants in Cd (5 mg·kg^-1) and Cd (10 mg·kg^-1) plus Pb treatments. Glutaric acid (30 mg·L^-1) could promote the translocation factors in the complex treatments of Cd (5 mg·kg^-1) with Pb (50, 100 mg·kg^-1) added. The application of citric and glutaric acid could be conducive to increase floral growth when proper doses are used, and incorporation of these organic acids can be a useful approach to assist cadmium and lead uptake by sunflower. However, growth, bioaccumulation, and translocation of metals may differ due to the metals' property, kinds, and concentrations of organic acids.

B" and C subunits of PP2A regulate the levels of reactive oxygen species and superoxide dismutase activities in Arabidopsis

The serine-threonine protein phosphatases PP2A regulate many cellular processes, however their role in oxidative stress responses and defence is less known. We show the involvement of its C (catalytic) and B" (a regulatory) subunits. The c3c4 (C subunit) and fass (B") subunit mutants and Col wt of Arabidopsis were used. Controls and treatments with the PP2A inhibitor microcystin-LR (MCY-LR) and reactive oxygen species (ROS) inducer diquat (DQ) were employed. ROS levels of primary roots were largely genotype dependent and both C and B" subunit mutants had increased sensitivity to MCY-LR and DQ indicating the involvement of these subunits in oxidative stress induction. Superoxide dismutases (SOD), mainly the Cu/Zn-SOD isoform, as key enzymes involved in ROS scavenging are also showing altered (mostly increased) activities in both c3c4 and fass mutants and have opposite relations to ROS induction. This indicates that the two types of subunits involved have partially different regulatory roles. In relation to this, control and MCY-LR/DQ treated B" subunit mutants were proven to have altered levels of phosphorylation of histone H2AX. γH2AX, the phosphorylated form indicates double stranded DNA damage during oxidative stress. Overall we point out the probable pivotal role of several PP2A subunits in the regulation of oxidative stress responses in plants and pave the way for future research to reveal the signaling pathways involved.

Silicon-mediated regulation of cadmium transport and activation of antioxidant defense system enhances Pennisetum glaucum resistance to cadmium stress

Pennisetum glaucum is an important forage grass for livestock. However, the large accumulation of cadmium (Cd) in plant tissues increases the risk of heavy metals entering the food chain in Cd-contaminated soils. Silicon (Si) can inhibit cadmium (Cd) uptake and enhance tolerance of plant to Cd toxicity, but whether and how Si alleviates Cd toxicity in grass and the underlying mechanisms are unclear. The present study explored the differential mechanisms of silicon-induced Cd transport in apoplast and symplast, Cd distribution in root tissue and antioxidant defense system in P. glaucum under Cd stress through hydroponic and pot experiments. The present results showed that exogenous Si supply significantly reduced Cd concentrations in apoplast and symplast; Si treatment increased monosilicic acid concentration in apoplast and symplast of the roots and shoots under Cd stress. Elemental analysis of root microdomains showed that Si treatment increased the distribution of Cd and Si in the endodermis by 42.6% and 14.0%, respectively. Si alleviated the adverse influences of Cd on plant growth, which were manifested in root morphological traits and root activity. In addition, Si addition significantly increased the activities of catalase and superoxide dismutase by 37.0% and 72.7%, and improved the efficiency of the ascorbate-glutathione cycle in Cd-stress shoots. Furthermore, Si significantly reduced the contents of hydrogen peroxide and superoxide anion in Cd-stressed shoots by 16.6% and 48.7%, respectively. These findings demonstrate that Si enhances the resistance of P. glaucum to Cd stress through regulating Cd transport pathways and activating antioxidant defense systems.

ROS Homeostasis Involved in Dose-Dependent Responses of Arabidopsis Seedlings to Copper Toxicity

As an essential element in plant nutrition, copper (Cu) can promote or inhibit plant growth depending on its concentration. However, the dose-dependent effects of copper, particularly on DNA damage associated with reactive oxygen species (ROS) homeostasis, are much less understood. In this work, we analyzed the dual effect of Cu (5, 20, and 60 μM) on the reproductive performance of Arabidopsis plants. Whereas Cu5 promoted inflorescence initiation and increased kilo seed weight, two higher concentrations, Cu20 and Cu60, delayed inflorescence initiation and negatively affected silique size. Excess Cu also induced changes in cellular redox homeostasis, which was examined by in situ visualization and measurements of ROS, including superoxide (O2•-), hydrogen peroxide (H2O2), malonyldialdehyde (MDA), and plasma membrane damage. The most dramatic increases in the production of O2•- and H2O2 along with increased activity of superoxide dismutase (SOD) and glutathione peroxidase (GPX) and decreased activity of catalase (CAT) and ascorbate peroxidase (APX) were observed in roots with Cu60. Oxidative stress also modulated the expression levels of a number of genes involved in the DNA damage response (DDR), particularly those related to DNA repair. The Cu-induced chlorosis of Arabidopsis seedlings could be alleviated by exogenous addition of glutathione (GSH) and ascorbate (Asc), as the chlorophyll content was significantly increased. Overall, internal homeostasis ROS and the associated DDR pathway and the corresponding scavenging mechanisms play a central role in the response of Arabidopsis to oxidative stress induced by inhibitory Cu concentrations. Our results have shown, for the first time, that the biphasic responses of Arabidopsis seedlings to increasing Cu concentrations involve different DNA damage responses and oxidative reactions. They provide the basis for elucidating the network of Cu-induced DDR-related genes and the regulatory mechanism of the complex ROS production and scavenging system.

Maize (Zea mays L.) responses to salt stress in terms of root anatomy, respiration and antioxidative enzyme activity

BACKGROUND

Soil salt stress is a problem in the world, which turns into one of the main limiting factors hindering maize production. Salinity significantly affects root physiological processes in maize plants. There are few studies, however, that analyses the response of maize to salt stress in terms of the development of root anatomy and respiration.

RESULTS

We found that the leaf relative water content, photosynthetic characteristics, and catalase activity exhibited a significantly decrease of salt stress treatments. However, salt stress treatments caused the superoxide dismutase activity, peroxidase activity, malondialdehyde content, Na⁺ uptake and translocation rate to be higher than that of control treatments. The detrimental effect of salt stress on YY7 variety was more pronounced than that of JNY658. Under salt stress, the number of root cortical aerenchyma in salt-tolerant JNY658 plants was significantly higher than that of control, as well as a larger cortical cell size and a lower root cortical cell file number, all of which help to maintain higher biomass. The total respiration rate of two varieties exposed to salt stress was lower than that of control treatment, while the alternate oxidative respiration rate was higher, and the root response of JNY658 plants was significant. Under salt stress, the roots net Na⁺ and K⁺ efflux rates of two varieties were higher than those of the control treatment, where the strength of net Na⁺ efflux rate from the roots of JNY658 plants and the net K⁺ efflux rate from roots of YY7 plants was remarkable. The increase in efflux rates reduced the Na⁺ toxicity of the root and helped to maintain its ion balance.

CONCLUSION

These results demonstrated that salt-tolerant maize varieties incur a relatively low metabolic cost required to establish a higher root cortical aerenchyma, larger cortical cell size and lower root cortical cell file number, significantly reduced the total respiration rate, and that it also increased the alternate oxidative respiration rate, thereby counteracting the detrimental effect of oxidative damage on root respiration of root growth. In addition, Na⁺ uptake on the root surface decreased, the translocation of Na⁺ to the rest of the plant was constrained and the level of Na⁺ accumulation in leaves significantly reduced under salt stress, thus preempting salt-stress induced impediments to the formation of shoot biomass.

Loss-of-function mutations of OsbHLH044 transcription factor lead to salinity sensitivity and a greater chalkiness in rice (Oryza sativa L.)

The most hazardous abiotic stress, salinity, restricted the world crop production, and grain chalkiness affected the grain quality to limit consumers' acceptance. The basic helix-loop-helix (bHLH) proteins modulate massive biological processes in plants. Here the CRISPR/Cas9 gene editing mutants were obtained to detect the function of OsbHLH044. The loss-of-function of OsbHLH044 mutants showed numerous altered plant phenotypes. Notably, the osbhlh044 mutants resulted in prominently reduced morphological and physiological parameters under salt stress. Lower antioxidant activities and higher lipid peroxidation and hydrogen peroxide (H₂O₂) accumulation in the osbhlh044 mutants caused salinity sensitivity due to elevated reactive oxygen species (ROS). Under salt stress, both shoots and roots of the osbhlh044 mutants acquired higher Na⁺. Moreover, the expression of ion homeostasis-related genes (OsHKTs, OsHAK, OsSOSs, and OsNHX) and ABA-responsive gene (OsLEA3) was significantly altered in the osbhlh044 mutants after salt stress. The expression levels of genes coding for starch (OsAGPL1, OsSSIIa, OsWx, and OsFLO2) and seed storage proteins (GluA1 and Globulin 1) were significantly decreased, indicating that they synthesize less store starch and proteins, resulting in grain chalkiness in the osbhlh044 mutants. Yeast one Hybrid (Y1H) showed that OsbHLH044 could activate salt- (OsHKT1;3, OsHAK7, OsSOS1, OsSOS2, OsNHX2, and OsLEA3 but not OsHKT2;1), and starch-related genes (OsSSIIa, OsWx, and OsFLO2) by binding to the G-boxes of their promoters. Therefore, the OsbHLH044 gene editing mutants revealed multiple functions, specifically a positive regulator of salt stress and grain quality, which might bring new insights into the breeding of rice varieties.

Are Foliar Nutrition Status and Indicators of Oxidative Stress Associated with Tree Defoliation of Four Mediterranean Forest Species?

Mediterranean forest ecosystems in Croatia are of very high significance because of the ecological functions they provide. This region is highly sensitive to abiotic stresses such as air pollution, high sunlight, and high temperatures alongside dry periods; therefore, it is important to monitor the state of these forest ecosystems and how they respond to these stresses. This study was conducted on trees in situ and focused on the four most important forest species in the Mediterranean region in Croatia: pubescent oak (Quercus pubescens Willd.), holm oak (Quercus ilex L.), Aleppo pine (Pinus halepensis Mill.) and black pine (Pinus nigra J. F. Arnold.). Trees were selected and divided into two groups: trees with defoliation of >25% (defoliated) and trees with defoliation of ≤25% (undefoliated). Leaves and needles were collected from selected trees. Differences in chlorophyll content, hydrogen peroxide content, lipid peroxidation and enzyme activity (superoxide dismutase, catalase, ascorbate peroxidase, non-specific peroxidase), and nutrient content between the defoliated and undefoliated trees of the examined species were determined. The results showed that there were significant differences for all species between the defoliated and undefoliated trees for at least one of the examined parameters. A principal component analysis showed that the enzyme ascorbate peroxidase can be an indicator of oxidative stress caused by ozone. By using oxidative stress indicators, it is possible to determine whether the trees are under stress even before visual damage occurs.

TMT-Based Comparative Peptidomics Analysis of Rice Seedlings under Salt Stress: An Accessible Method to Explore Plant Stress-Tolerance Processing

Rice (Oryza sativa L.) is an important staple crop, particularly in Asia, and abiotic stress conditions easily reduce its yields. Salt stress is one of the critical factors affecting rice growth and yield. In this study, a tandem mass tag (TMT)-based comparative peptidomics analysis of rice seedlings under salt stress was conducted. Rice seedlings were exposed to 50 and 150 mM NaCl for 24 and 72 h, respectively, and the root and shoot tissues of different treatment groups were collected separately for peptidomics analysis. A total of 911 and 1263 nonredundant peptides were identified in two pooled shoot tissue samples, while there were 770 and 672 nonredundant peptides in two pooled root tissue samples, respectively. Compared with the control groups, dozens to hundreds of differentially expressed peptides (DEPs) were characterized in all treatment groups. To explore the potential functions of these DEPs, we analyzed the basic characteristics of DEPs and further analyzed the annotated Gene Ontology terms according to their precursor proteins. Several DEP precursor proteins were closely related to the response to salt stress, and some were derived from the functional domains of their corresponding precursors. The germination rate and cotyledon greening rate of transgenic Arabidopsis expressing two DEPs, OsSTPE2 and OsSTPE3, were significantly enhanced under salt stress. The described workflow enables the discovery of a functional pipeline for the characterization of the plant peptidome and reveals two new plant peptides that confer salinity tolerance to plants. Data are available via ProteomeXchange with identifier PXD037574.

Overexpression of a Malus baccata CBF transcription factor gene, MbCBF1, Increases cold and salinity tolerance in Arabidopsis thaliana

CBFs play a crucial role when plants are in adverse environmental conditions for growth. However, there are few reports on the role of CBF gene in stress responses of Malus plant. In this experiment, a new CBF TF was separated from M. baccata which was named MbCBF1. MbCBF1 protein was found to be localized in the nucleus after subcellular localization. Furthermore, the expression of MbCBF1 was highly accumulated in new leaves and roots due to the high influence of cold and high salt in M. baccata seedlings. After introducing MbCBF1 into A. thaliana, transgenic A. thaliana can better adapt to the living conditions of cold and high salt. The increased expression of MbCBF1 in A. thaliana also increased the contents of proline, remarkablely improved the activities of SOD, POD and CAT, but the content of MDA was decreased. Although the chlorophyll content also decreased, it decreased less in transgenic plants. In short, above date showed that MbCBF1 has a positive effect on improving A. thaliana cold and high salt tolerance. MbCBF1 can regulate the expression of its downstream gene in transgenic lines, up-regulate the expression of key genes COR15a, RD29a/bandCOR6.6/47 related to low temperature under cold conditions and NCED3, CAT1, P5CS1, RD22, DREB2A,PIF1/4, SOS1 and SnRK2.4 related to salt stress under high salt conditions, so as to further improve the adaptability and tolerance of the transgenic plants to low temperature and high salt environment.

Conventional and Omics Approaches for Understanding the Abiotic Stress Response in Cereal Crops-An Updated Overview

Cereals have evolved various tolerance mechanisms to cope with abiotic stress. Understanding the abiotic stress response mechanism of cereal crops at the molecular level offers a path to high-yielding and stress-tolerant cultivars to sustain food and nutritional security. In this regard, enormous progress has been made in the omics field in the areas of genomics, transcriptomics, and proteomics. Omics approaches generate a massive amount of data, and adequate advancements in computational tools have been achieved for effective analysis. The combination of integrated omics and bioinformatics approaches has been recognized as vital to generating insights into genome-wide stress-regulation mechanisms. In this review, we have described the self-driven drought, heat, and salt stress-responsive mechanisms that are highlighted by the integration of stress-manipulating components, including transcription factors, co-expressed genes, proteins, etc. This review also provides a comprehensive catalog of available online omics resources for cereal crops and their effective utilization. Thus, the details provided in the review will enable us to choose the appropriate tools and techniques to reduce the negative impacts and limit the failures in the intensive crop improvement study.

Genome-wide identification of the rubber tree superoxide dismutase (SOD) gene family and analysis of its expression under abiotic stress

Background

The rubber tree (Hevea brasiliensis) is the only species capable of producing high-quality natural rubber for commercial use, and is often subjected to various abiotic stresses in non-traditional rubber plantation areas. Superoxide dismutase (SOD) is a vital metalloenzyme translated by a SOD gene family member and acts as a first-line of protection in plant cells by catalysing the disproportionation of reactive oxygen species (ROS) to produce H₂O₂ and O₂. However, the SOD gene family is not reported in rubber trees.

Methods

Here, we used hidden markov model (HMM) and BLASTP methods to identify SOD genes in the H. brasiliensis genome. Phylogenetic tree, conserved motifs, gene structures, cis elements, and gene ontology annotation (GO) analyses were performed using MEGA 6.0, MEME, TBtools, PlantCARE, and eggNOG database, respectively. HbSOD gene expression profiles were analysed using quantitative reverse transcription polymerase chain reaction (qRT-PCR).

Results

We identified nine HbSOD genes in the rubber tree genome, including five HbCSDs, two HbFSDs, and two HbMSDs. Phylogenetic relationship analysis classified the SOD proteins from the rubber tree and other related species into three subfamilies. The results of gene structure and conserved motif analysis illustrated that most HbSOD genes have similar exon-intron numbers and conserved motifs in the same evolutionary branch. Five hormone-related, four stress-related, and light-responsive elements were detected in the HbSODs' promoters. HbSODs were expressed in different tissues, gradually increased with leaf development, and were abundantly expressed in mature leaves. HbCSD2 and HbCSD4 was significantly upregulated under low and high temperatures, and salt stress, except for HbCSD2, by heat. Furthermore, most HbSOD genes were significantly upregulated by drought, except HbMSD2. These findings imply that these genes may play vital roles in rubber tree stress resistance. Our results provide a basis for further studies on the functions of HbSOD genes in rubber trees and stress response mechanisms.

Crosstalk of nitro-oxidative stress and iron in plant immunity

Accumulation of oxygen and nitrogen radicals and their derivatives, known as reactive oxygen species (ROS) and reactive nitrogen species (RNS), occurs throughout various phases of plant growth in association with biotic and abiotic stresses. One of the consequences of environmental stresses is disruption of homeostasis between production and scavenging of ROS and RNS, which leads to nitro-oxidative burst and affects other defense-related mechanisms, such as polyamines levels, phenolics, lignin and callose as defense components related to plant cell wall reinforcement. Although this subject has attracted huge interest, the cross-talk between these signaling molecules and iron, as a main metal element involved in the activity of various enzymes and numerous vital processes in the living cells, remains largely unexplored. Therefore, it seems necessary to pay more in depth attention to the mechanisms of plant resistance against various environmental stimuli for designing novel and effective plant protection strategies. This review is focused on advances in recent knowledge related to the role of ROS, RNS, and association of these signaling molecules with iron in plant immunity. Furthermore, the role of cell wall fortification as a main physical barrier involved in plant defense have been discussed in association with reactive species and iron ions.

Insights to the superoxide dismutase genes and its roles in Hevea brasiliensis under abiotic stress

The superoxide dismutase (SOD) protein significantly influences the development and growth of plants and their reaction to abiotic stresses. However, little is known about the characteristics of rubber tree SOD genes and their expression changes under abiotic stresses. The present study recognized 11 SOD genes in the rubber tree genome, including 7 Cu/ZnSODs, 2 MnSODs, and 2 FeSODs. Except for HbFSD1, SODs were scattered on five chromosomes. The phylogenetic analysis of SOD proteins in rubber trees and a few other plants demonstrated that the SOD proteins contained three major subgroups. Moreover, the genes belonging to the same clade contained similar gene structures, which confirmed their classification further. The extension of the SOD gene family in the rubber tree was mainly induced by the segmental duplication events. The cis-acting components analysis showed that HbSODs were utilized in many biological procedures. The transcriptomics data indicated that the phosphorylation of the C-terminal domain of RNA polymerase II might control the cold response genes through the CBF pathway and activate the SOD system to respond to cold stress. The qRT-PCR results showed that the expression of HbCSD1 was significantly downregulated under drought and salt stresses, which might dominate the adaption capability to different stresses. Additionally, salt promoted the expression levels of HbMSD1 and HbMSD2, exhibiting their indispensable role in the salinity reaction. The study results will provide a theoretical basis for deep research on HbSODs in rubber trees.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03328-7.

Influence of cadmium and microplastics on physiological responses, ultrastructure and rhizosphere microbial community of duckweed

The combined contamination of heavy metals and microplastics is widespread in freshwater environments. However, there are few researches on their combined effects on aquatic plants. In this study, the effects of single and combined stress of 0.01 mg L^-1 cadmium (Cd), 50 mg L^-1 polyethylene and 50 mg L^-1 polypropylene for 15 days on the physiological response, ultrastructure and rhizosphere microbial community of duckweed were investigated. The results showed that Cd and microplastics single or combined stress inhibited the growth of duckweed, shortened the root length and decreased the chlorophyll content. Compared with single Cd treatments, the combination of microplastics and Cd increased duckweed growth rate and increased superoxide dismutase activity and malondialdehyde content and reduced chloroplast structural damage, indicating that the combined stress could reduce the toxicity of heavy metals to duckweed. Through the study of rhizosphere microbial diversity, 1381 Operational Taxonomic Unit (OTUs) were identified and rich microbial communities were detected in the duckweed rhizosphere. Among them, the main microbial communities were Proteobacteria, Bacteroidetes, and Cyanobacteria. Compared with Cd single stress, the ACE and chao index of rhizosphere microbial community increased under combined stress, indicating that the diversity and abundance of microbial communities were improved after combined stress treatment. Our study revealed the effects of heavy metals and microplastics on aquatic plants, providing a theoretical basis for duckweed applications in complex water pollution.

Comparative Study of Trehalose and Trehalose 6-Phosphate to Improve Antioxidant Defense Mechanisms in Wheat and Mustard Seedlings under Salt and Water Deficit Stresses

Trehalose 6-phosphate (T6P) regulates sugar levels and starch metabolism in a plant cell and thus interacts with various signaling pathways, and after converting T6P into trehalose (Tre), it acts as a vital osmoprotectant under stress conditions. This study was conducted using wheat (Triticum aestivum L. cv. Norin 61) and mustard (Brassica juncea L. cv. BARI sharisha 13) seedlings to investigate the role of Tre and T6P in improving salt and water deficit stress tolerance. The seedlings were grown hydroponically using Hyponex solution and exposed to salt (300 and 200 mM NaCl for wheat and mustard, respectively) and water deficit (20 and 12% PEG 6000 for wheat and mustard, respectively) stresses with or without Tre and T6P. The study demonstrated that salt and water deficit stress negatively influenced plant growth by destroying photosynthetic pigments and increasing oxidative damage. In response to salt and water deficit stresses, the generation of H2O2 increased by 114 and 67%, respectively, in wheat seedlings, while in mustard, it increased by 86 and 50%, respectively. Antioxidant defense systems were also altered by salt and water deficit stresses due to higher oxidative damage. The AsA content was reduced by 65 and 38% in wheat and 61 and 45% in mustard under salt and water deficit stresses, respectively. The subsequent negative results of salinity and water deficit can be overcome by exogenous application of Tre and T6P; these agents reduced the oxidative stress by decreasing H2O2 and TBARS levels and increasing enzymatic and non-enzymatic antioxidants. Moreover, the application of Tre and T6P decreased the accumulation of Na in the shoots and roots of wheat and mustard seedlings. Therefore, the results suggest that the use of Tre and T6P is apromising strategy to alleviate osmotic and ionic toxicity in plants under salt and water deficit stresses.

Isolation and Functional Analysis of MbCBF2, a Malus baccata (L.) Borkh CBF Transcription Factor Gene, with Functions in Tolerance to Cold and Salt Stress in Transgenic Arabidopsis thaliana

CBF transcription factors (TFs) are key regulators of plant stress tolerance and play an integral role in plant tolerance to adverse growth environments. However, in the current research situation, there are few reports on the response of the CBF gene to Begonia stress. Therefore, this experiment investigated a novel CBF TF gene, named MbCBF2, which was isolated from M. baccata seedlings. According to the subcellular localization results, the MbCBF2 protein was located in the nucleus. In addition, the expression level of MbCBF2 was higher in new leaves and roots under low-temperature and high-salt induction. After the introduction of MbCBF2 into Arabidopsis thaliana, the adaptability of transgenic A. thaliana to cold and high-salt environments was significantly enhanced. In addition, the high expression of MbCBF2 can also change many physiological indicators in transgenic A. thaliana, such as increased chlorophyll and proline content, superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) activity, and reduced malondialdehyde (MDA) content. Therefore, it can be seen from the above results that MbCBF2 can positively regulate the response of A. thaliana to low-temperature and osmotic stress. In addition, MbCBF2 can also regulate the expression of its downstream genes in transgenic lines. It can not only positively regulate the expression of the downstream key genes AtCOR15a, AtERD10, AtRD29a/b and AtCOR6.6/47, related to cold stress at low temperatures, but can also positively regulate the expression of the downstream key genes AtNCED3, AtCAT1, AtP5CS, AtPIF1/4 and AtSnRK2.4, related to salt stress. That is, the overexpression of the MbCBF2 gene further improved the adaptability and tolerance of transgenic plants to low-temperature and high-salt environments.

Transcriptome Analysis Provides Insights into Potentilla bifurca Adaptation to High Altitude

Potentilla bifurca is widely distributed in Eurasia, including the Tibetan Plateau. It is a valuable medicinal plant in the Tibetan traditional medicine system, especially for the treatment of diabetes. This study investigated the functional gene profile of Potentilla bifurca at different altitudes by RNA-sequencing technology, including de novo assembly of 222,619 unigenes from 405 million clean reads, 57.64% of which were annotated in Nr, GO, KEGG, Pfam, and Swiss-Prot databases. The most significantly differentially expressed top 50 genes in the high-altitude samples were derived from plants that responded to abiotic stress, such as peroxidase, superoxide dismutase protein, and the ubiquitin-conjugating enzyme. Pathway analysis revealed that a large number of DEGs encode key enzymes involved in secondary metabolites, including phenylpropane and flavonoids. In addition, a total of 298 potential genomic SSRs were identified in this study, which provides information on the development of functional molecular markers for genetic diversity assessment. In conclusion, this study provides the first comprehensive assessment of the Potentilla bifurca transcriptome. This provides new insights into coping mechanisms for non-model organisms surviving in harsh environments at high altitudes, as well as molecular evidence for the selection of superior medicinal plants.

Functional Characterization of MaZIP4, a Gene Regulating Copper Stress Tolerance in Mulberry (Morus atropurpurea R.)

ZIP4 (zinc transporter 4) plays important roles in transporting Cu²⁺ ions in plants, which may contribute to the maintenance of plant metal homeostasis in growth, plant development and normal physiological metabolism. However, ZIP4 transporters have not been described in mulberry and the exact function of ZIP4 transporters in regulating the homeostasis of Cu in mulberry remains unclear. In this study, a new ZIP4 gene (MaZIP4) was isolated and cloned from Morus atropurpurea R. Phylogenetic analysis of amino sequences suggested that the amino-acid sequence of the MaZIP4 protein shows high homology with other ZIP4 proteins of Morus notabilis, Trema orientale, Ziziphus jujube and Cannabis sativa. In addition, a MaZIP4 silenced line was successfully constructed using virus-induced gene silencing (VIGS). The analysis of MaZIP4 expression by quantitative real-time PCR in mulberry showed that the level of MaZIP4 expression increased with increasing Cu concentration until the Cu concentration reached 800 ppm. Relative to the blank (WT) and the negative controls, malondialdehyde (MDA) levels increased significantly and rose with increasing Cu concentration in the MaZIP4 silenced line, whereas the soluble protein and proline content, superoxide dismutase (SOD) and peroxidase (POD) activities of these transgenic plants were lower. These results indicated that MaZIP4 may play an important role in the resistance of mulberry to Cu stress.

Silicon-mediated metabolic upregulation of ascorbate glutathione (AsA-GSH) and glyoxalase reduces the toxic effects of vanadium in rice

Although beneficial metalloid silicon (Si) has been proven to reduce the toxicity of several heavy metals, there is a lack of understanding regarding Si potential function in mitigating phytotoxicity induced by vanadium (V). In this study, effect of Si (1.5 mM) on growth, biomass production, V uptake, reactive oxygen species (ROS), methylglyoxal (MG) formation, selected antioxidants enzymes activities, glyoxalase enzymes under V stress (35 mg L^-1) was investigated in hydroponic experiment. The results showed that V stress reduced rice growth, caused V accumulation in rice. Addition of Si to the nutritional medium increased plant growth, biomass yield, root length, root diameter, chlorophyll parameters, photosynthetic assimilation, ion leakage, antioxidant enzymes activities under V stress. Notably, Si sustained V-homeostasis and alleviated V caused oxidative stress by boosting ascorbate (AsA) levels and the activity of antioxidant enzymes in V stressed rice plants. Furthermore, Si protected rice seedlings against the harmful effects of methylglyoxal by increasing the activity of glyoxalase enzymes. Additionally, Si increased the expression of numerous genes involved in the detoxification of reactive oxygen species (e.g., OsCuZnSOD1, OsCaTB, OsGPX1, OsAPX1, OsGR2, and OsGSTU37) and methylglyoxal (e.g., OsGLYI-1 and OsGLYII-2). The findings supported that Si can be applied to plants to minimize the V availability to plant, and also induced V stress tolerance.

Mnsod1 promotes the development of Pleurotus ostreatus and enhances the tolerance of mycelia to heat stress

Background

Superoxide dismutases (SODs, EC 1.15.1.1) are defense proteins that can be used as sweepers to clear reactive oxygen species (ROS). They have been widely studied in the plant. Intensive research demonstrates that SOD plays an essential role in plants. However, in Pleurotus ostreatus, the function and regulatory pathway of SOD in the growth and development and the abiotic stress response have not been clear.

Results

In this study, three MnSOD-encoding genes of the P. ostreatus CCMSSC00389 strain were cloned and identified. Mnsod1, Mnsod2, and Mnsod3 were interrupted by 3, 7, and 2 introns, and encoded proteins of 204, 220, and 344 amino acids, respectively. By comparing the relative expression of three MnSOD-encoding genes in mycelia, the results showed that the gene with the highest primary expression was Mnsod1. Subsequently, the function of P. ostreatus Mnsod1 was explored by overexpression (OE) and RNA interference (RNAi). The results showed that during the growth and development of P. ostreatus, MnSOD1 protein increased gradually from mycelia to the fruiting body, but decreased in spores. The change of Mnsod1 transcription level was not consistent with the changing trend of MnSOD1 protein. Further studies showed that during primordia formation, the expression of Mnsod1 gradually increased, reaching a peak at 48 h, and the transcription level was 2.05-folds compared to control. H₂O₂ content progressively accumulated during the formation of primordia, and its change trend was similar to that of Mnsod1 transcription. OE-Mnsod1-1 and OE-Mnsod1-21 strains accelerated the formation of primordia. The results suggested that Mnsod1 may participate in the formation rate of P. ostreatus primordium by regulating the signal molecule H₂O₂. In addition, OE-Mnsod1-1 and OE-Mnsod1-21 strains shortened the mycelial recovery time after heat stress and improved the tolerance of the strains to 2.5 mM and 5 mM H₂O₂, which showed that Mnsod1 was involved in the response of P. ostreatus mycelium to heat stress.

Conclusions

This study indicates that Mnsod1 plays an active role in the formation of P. ostreatus primordia and the response to abiotic stress.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-022-01878-2.

Effects of extraction methods for a new source of biostimulant from Sargassum horneri on the growth of economically important red algae, Neopyropia yezoensis

Sargassum horneri is a major bloom forming species in Korea and China. It is important to find a way to utilize the huge biomass of Sargassum horneri in the region. Seaweed-derived biostimulants are primarily derived from brown algae and are known to improve terrestrial crop growth and tolerance to abiotic stresses. Neopyropia yezoensis is the most important seaweed cultured species in Korea, and research is required to increase heat resistance as a solution against climate change. In this study, various extraction methods were used to obtain Sargassum horneri extract, and it was applied to Neopyropia yezoensis to evaluate the effect on physiological activity. Metabolites of Sargassum horneri were extracted by using four different methods: boiling (SBE), soaking (SSE), autoclaving (SAE) and ethanol (SEE). The SBE, SSE and SAE derived extracts showed increased tolerance to high-temperature stress that had inhibited the growth of Neopyropia yezoensis, and show improved growth compared to the control group. The SBE and SSE extraction methods improved the content of phycobiliprotein, but also the SBE increased superoxide dismutase (SOD) activity. Based on the results of this study, the boiling extraction method appears to be the most suitable method for the extraction of plants stimulants from Sargassum horneri.

Transgenic tobacco co-expressing flavodoxin and betaine aldehyde dehydrogenase confers cadmium tolerance through boosting antioxidant capacity

Excessive heavy metal (HM) levels in soil have become a source of concern due to their adverse effects on human health and the agriculture industry. Soil contamination by HMs leads to an accumulation of reactive oxygen species (ROSs) within the plant cell and disruption of photosynthesis-related proteins. The response of tobacco lines overexpressing flavodoxin (Fld) and betaine aldehyde dehydrogenase (BADH) to cadmium (Cd) toxicity was investigated in this study. PCR results demonstrated the expected amplicon length of each gene in the transgenic lines. Absolute qRT-PCR demonstrates a single copy of T-DNA integration into each transgenic line. Relative qRT-PCR confirmed overexpression of Fld and BADH in transgenic lines. The maximum quantum yield of photosystem II (Fv/Fm) was measured under Cd toxicity stress and revealed that transgenic lines had a higher Fv/Fm than wild-type (WT) plants. Accumulation of proline, glycine betaine (GB), and higher activity of antioxidant enzymes alongside lower levels of malondialdehyde (MDA) and hydrogen peroxide (H2O2) was indicative of a robust antioxidant system in transgenic plants. Therefore, performing a loop in reducing the ROS produced in the photosynthesis electron transport chain and stimulating the ROS scavenger enzyme activity improved the plant tolerance to Cd stress.

Molecular Evolution and Functional Divergence of Stress-Responsive Cu/Zn Superoxide Dismutases in Plants

Superoxide dismutases (SODs), a family of antioxidant enzymes, are the first line of defense against oxidative damage and are ubiquitous in every cell of all plant types. The Cu/Zn SOD, one of three types of SODs present in plant species, is involved in many of the biological functions of plants in response to abiotic and biotic stresses. Here, we carried out a comprehensive analysis of the Cu/Zn SOD gene family in different plant species, ranging from lower plants to higher plants, and further investigated their organization, sequence features, and expression patterns in response to biotic and abiotic stresses. Our results show that plant Cu/Zn SODs can be divided into two subfamilies (group I and group II). Group II appeared to be conserved only as single- or low-copy genes in all lineages, whereas group I genes underwent at least two duplication events, resulting in multiple gene copies and forming three different subgroups (group Ia, group Ib, and group Ic). We also found that, among these genes, two important events—the loss of introns and the loss of and variation in signal peptides—occurred over the long course of their evolution, indicating that they were involved in shifts in subcellular localization from the chloroplast to cytosol or peroxisome and underwent functional divergence. In addition, expression patterns of Cu/Zn SOD genes from Arabidopsis thaliana and Solanum lycopersicum were tested in different tissues/organs and developmental stages and under different abiotic stresses. The results indicate that the Cu/Zn SOD gene family possesses potential functional divergence and may play vital roles in ROS scavenging in response to various stresses in plants. This study will help establish a foundation for further understanding these genes’ function during stress responses.

Molecular and Biochemical Analysis of Duplicated Cytosolic CuZn Superoxide Dismutases of Rice and in silico Analysis in Plants

Superoxide dismutases (SODs, EC 1.15.1.1) are ubiquitous antioxidant metalloenzymes important for oxidative stress tolerance and cellular redox environment. Multiple factors have contributed toward the origin and diversity of SOD isoforms among different organisms. In plants, the genome duplication events, responsible for the generation of multiple gene copies/gene families, have also contributed toward the SOD diversity. However, the importance of such molecular events on the characteristics of SODs has not been studied well. This study investigated the effects of divergence on important characteristics of two block-duplicated rice cytosolic CuZn SODs (OsCSD1, OsCSD4), along with in silico assessment of similar events in other plants. The analysis revealed heterogeneity in gene length, regulatory regions, untranslated regions (UTRs), and coding regions of two OsCSDs. An inconsistency in the database-predicted OsCSD1 gene structure was also identified and validated experimentally. Transcript analysis showed differences in the basal levels and stress responsiveness of OsCSD1 and OsCSD4, and indicated the presence of two transcription start sites in the OsCSD1. At the amino acid level, the two OsCSDs showed differences at 18 sites; however, both exist as a homodimer, displaying typical CuZn SOD characteristics, and enhancing the oxidative stress tolerance of Escherichia coli cells. However, OsCSD4 showed higher specific activity as well as stability. The comparison of the two OsCSDs with reported thermostable CSDs from other plants identified regions likely to be associated with stability, while the homology modeling and superposition highlighted structural differences. The two OsCSDs displayed heteromeric interaction capability and forms an enzymatically active heterodimer (OsCSD1:OsCSD4) on co-expression, which may have significance as both are cytosolic. In silico analysis of 74 plant genomes revealed the prevalence of block duplications for multiple CSD copies (mostly cytosolic). The divergence and clustering analysis of CSDs suggested the possibility of an ancestral duplication event in monocots. Conserved SOD features indicating retention of SOD function among CSD duplicates were evident in few monocots and dicots. In most other species, the CSD copies lacked critical features and may not harbor SOD function; however, other feature-associated functions or novel functions might be present. These aspects of divergent CSD copies encoding co-localized CSDs may have implications in plant SOD functions in the cytosol and other organelles.